A hernia is an abnormal protrusion of a peritoneal-lined sac through the musculo-aponeurotic covering of the abdomen, the most common site for a hernia being the groin. Types of hernias are, among others, inguinal hernia or femoral hernia, hiatal hernia, umbilical hernia and incisional hernia, the latter being a hernia that pushes through a past surgical incision or operation site.
Hernias are repaired by a surgical procedure where the protrusion is retracted to its original position within the abdominal cavity, and subsequent healing is facilitated by covering the abdominal wall defect with a surgical implant. This can be done under local or general anesthesia using a laparoscope or an open incision technique.
Within the field of surgical repair of soft tissue defects such as hernias, use is often made of a mesh implant fabricated of a non-resorbable material that is inserted to cover the area of the tissue defect without sewing together the surrounding muscles. The mesh implant is used in order to support the regenerating tissue and works by mechanical closure of the defect as well as by inducing a strong scar fibrous tissue around the mesh implant. Such a mesh implant is most often made of various plastics, which are known to stay biostable and safe for a number of years after implantation. However, measurements of nine common mesh materials show a lower elasticity (with a mean value of approximately 15%) than that of the intact abdominal wall (23-32%) (K. Junge et al.: Elasticity of the anterior abdominal wall and impact for reparation of incisional hernias using mesh implants. Hernia 2001, no. 5, p. 113-118), which could result in discomfort, inflammation and recurrence of the hernia. Furthermore, permanently introducing a foreign material into the human or animal body could be accompanied with side effects such as migration, chronic inflammation, risk of infection, etc. The introduction of a relatively large inert implant is also likely to induce a long-term foreign body-reaction caused by the body's immune defense system. As a result, the mesh implant may crumple up and lose its tissue supporting function.
A solution to this is described in U.S. Pat. No. 6,319,264 which describes a porous, flexible and fibrous hernia mesh comprising two functional layers, wherein the first layer is a rapidly degradable polymer layer facing the fascia, and wherein the second layer is a more slowly degradable polymer layer. The mesh described in U.S. Pat. No. 6,319,264 acts as a temporary support until connective scar tissue has strengthened enough and can replace the mesh, when the second layer finally degrades. However, U.S. Pat. No. 6,319,264 is silent as to the load situation found over the tissue defect area and to any related adjustment of the relative distension of the hernia mesh.
Patent application EP 0797962 describes a mesh implant with a basic structure made from a knitted fabric comprising non-resorbable material or resorbable material, wherein the mesh is designed to stretch to allow movement in the underlying tissue. To ease the procedure of cutting and handling the mesh prior to insertion, the basic structure can be strengthened by adding a stiffener. The stiffener comprises a resorbable material which is either coated onto the knitted fibers or supplied as fibers which are woven together with (i.e. in the same pattern as) the fibers of the basic structure. This stiffening material is designed to resorb soon after surgery. However, the mesh implant provided in patent application EP 0797962 offers no particular measures to facilitate the primary formation of fibrotic tissue during the early stages of wound healing.
The U.S. Patent Application No. 2006/0142786, which is assigned to the present assignee, describes a mesh implant of a resorbable polymer comprising at least two materials, wherein the second material is substantially degraded at a later point in time than the first material following the time of implantation. The mesh implant is adapted to have a predetermined modulus of elasticity that gradually is decreased until the implant is completely degraded and subsequently absorbed. Due to the gradual decrease in the modulus of elasticity of the inventive mesh implant, the regenerating tissue may progressively take over the load applied to the tissue defect area. The U.S. Patent Application No. 2006/0142786 describes using materials with different elasticity overlaid on each other to achieve a gradual change in overall elasticity of the implant. To tailor for the properties of a mesh by choosing different materials may, however, in the case of a resorbable mesh be difficult, since the selection of suitable material commercially available is limited. In addition, these materials may be expensive and/or difficult to handle during the manufacturing of the mesh. The entire contents of U.S. Patent Application No. 2006/0142786 is incorporated herein by reference for the devices, techniques, and methods disclosed therein.
Consequently, there is still a need for an improved mesh implant which facilitates the healing process by relieving the tissue during initial stages of healing and allows the regenerating tissue to gradually take over the load during the progression of healing. It is therefore an object of the present invention to provide such a mesh implant which is completely degradable.